Method of softening plastic sheets



Patented May 23, 1939 STATE METHOD or s This invention relates to solvent compositions and more particularly to newsolvents for use in temporary softening of It is known that in plastics in coverin covering such objec hamper tops, high necessary first to sof condition such that and fitted to the objec softening. of the plas to. cover the mold .or .drying, or e terial shrink used, clings tenacious By nitrocellulose .trates .with which and/or other plas oil, tricresyl phosphat .or, generally, such as those of nitrocellulose plastics.

the use of nitrocellulose tions, particularly in ts as wood heels, toilet seats, hair trays, and the like, it is ten the plastic to a pliable it may be readily worked t to be covered. After it is easily stretched the form desired, and upon vaporation of the softener, the mas and, particularly when cement is ly to the object covered. tics I mean cellulose nihas been incorporated camphor ticizing agents such as castor e, diacetone and the like, nitrocellulose-containin the types represented by mates known under the trade-marked names Pyralin, Celluloid, Fibreloid, Lucite,

tures of solvents have f temporarily ls, but due to the particurtial solvent effect,

Various solvents and mix been proposed for the purpose 0 softening such materia lar limitations as to only pa softening effect upon the plastic, and rela or evaporation rate after applicad necessary in the past to e deleterious effects upon Thus, altho many mat the present invention, the found preferable has been of methanol and acetone in e softened but lution of these er than partially disthis aqueous solution epresenting as it does tory as to its softend evaporation rate, terized by several dis- Thus, this solvent has an immersed, or par the importance 0 able. Furthermore, suc

utions dissolve out considerable quantiwhich in turn necessitates the e solvent so that the tion of the solvent,

ties of camphor, addition of camphor to th plastic may, after evapora s PATENT OFFICE OFTENING PLASTIC SHEETS Julius F. T. Berliner, Wilmington, Del assignor to E. I. du Pont de Nemour's & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application May 9, 1935, Serial No. 20,603

have the same constitution as before treatment.

It is an object of this invention to overcome these and other disadvantages of the prior art and to produce a new and improved solvent.

new method of softening nitrocellulose plastics.

,Qther objects and advantages of the invention will be apparent by reference to the following specification inwhich its preferred embodiments and details are set forth.

Another object of the invention is to provide a;- 5

According to this invention nitrocellulose plastics may be advantageously softened by use of a solution of methanol and higher ketones which are immiscible or at least only partly miscible with water. This softening solution may be usedJB alone, altho I prefer, as is the case in the methanol-acetone solutions, to dilute the softener with water so that the final composition is constituted of from 3-4 parts by volume of methanol-higher ketone solution per part of water, preferably,

about 3.25 parts solvent per part of water.

The higher ketones which I have found to be so advantageous are those generally of from 4 to 9 carbon atoms per molecule and particularly those which are obtainable by the oxidation or;

dehydrogenation of the mixture of. branched chain secondary alcohols, obtainable by the catalytic pressure hydrogenation of oxide of carbon. Although mixtures of higher ketones generally and the complete mixture of ketones obtainable;

as above described are desirable and give superior results when mixed with methanol, 1'. have found that best results are obtained by use of one or more of those ketones obtainable by oxidation or dehydrogenation of the branched-chain secondary alcohols obtainable as above described, or a mixture of them, which have boiling ranges between 115-128 0., namely, methyl isopropyl, ethyl isopropyl and diisopropyl ketones. The ketone, such as diisopropyl ketone, or the mixture of boiling point range 115-128 C. is mixed with methanol in the proportions of from about 9 to 25 parts, preferably about 13 parts, by volume ketone to about '75 to 91 parts, preferably about 87 parts, methanol. Preferably 3%, parts of this solution is diluted with about one part of water before use.

Into such a solution is dipped a sheet of cellu lose plastic which is softened therein for about 30 minutes. At the expiration of this soaking the completely pliable sheet is removed from the softening bath, cement applied to the form or ering becomes hard and if left over night will be found to be ready for use, the major part if not all of the solvent having evaporated.

The material of this invention has no deleterious effect upon the hands of the operator, has a lower evaporation rate, which is more satisfactory from an operating standpoint, and sustains its strength for a longer time than materials previously used extensively, and, since camphor is not appreciably soluble therein, obviates the necessity of adding camphor to the softener to keep stable the plasticizer content of the nitrocellulose being treated.

I have found that the softener of this invention is generally easier to use for covering operations and, at the same time that more satisfactory results are obtained, a lower ketone content (corresponding to the acetone in previously used softeners) is possible than with methanol-acetone solutions heretofore used in industry.

The composition of this invention may be used advantageously in all operations which involve temporary softening of nitrocellulose plastics for whatever purpose it is desired, but is particularly suited for leather belt compositing, production of nitrocellulose plastic novelties, for covering operations such as previously set forth, and the like, wherein, for a short time at least, such plastics must be pliable and workable.

By utilizing the softener of this invention nitrocellulose plastics are made as soft and pliable as wet chamois and can be easily stretched to fit and cemented to whatever form desired.

Cellulose nitrate sheeting softened by the material of this invention has a better body than obtained with other material shows little or no tendency to curl, takes a cleaner, sharper embossing, remains in workable condition for a longer time, has less tendency to crack or split after application to wood heels or the like, and, importantly, is wholly free from the toxic effect upon the operator which is such a disadvantageous characteristic of previous softening solutions. Furthermore, as an economical advantage, the material of this invention has a slower rate of evaporation than other softeners and is less inflammable.

Various changes may be made in the present invention without departing therefrom or sacrificing any of the advantages thereof.

I claim:

1. In plastic sheeting operations, the method of softening but not dissolving sheeting of nitrocellulose plastic compositions which comprises treating such compositions with a solution of about one part by volume of water and 3 to 4 parts of a solution containing about 75 to 91 parts of methanol and about 9 to 25 parts of a relatively Water-immiscible ketone of from 4 to 9 carbon atoms per molecule having a boiling point in the range of about 115-128" C. and obtainable by oxidation of the secondary branched chain aliphatic alcohols produced by the catalytic pressure hydrogenation of oxide of carbon.

2. In plastic sheeting operations, the method of softening but not dissolving sheeting of nitrocellulose plastic compositions which comprises treating such compositions with a solution of about one part by volume of water and 3 to 4 parts of a solution comprising about 87 parts of methanol and about 13 parts of a relatively water-irnmiscible ketcne of from 4 to 9 carbon atoms per molecule, having a boiling point in the range of about l15l28 C., and obtainable by oxidation of the secondary branched chain aliphatic alcohols produced by the catalyticpressure hydrogenation of oxide of carbon.

3. In plastic sheeting operations, the method of softening but not dissolving sheeting of nitrocellulose plastic compositions which comprises treating such compositions with a solution of about one part by volume of water and 3 to 4 parts of a solution containing about 75 to 91 parts of methanol and about 9 to 25 parts of the mixture of methyl and ethyl isopropyl, and diisopropyl ketones obtainable by oxidation of the secondary branched chain aliphatic alcohols produced by the catalytic pressure hydrogenation of oxide of carbon.

4. In plastic sheeting operations, the method of softening but not dissolving sheeting of nitrocellulose plastic compositions which comprises treating such compositions with a solution of about one part by volume of water and 3 to 4 parts of methanol and about 13 parts of the mixture of methyl and ethyl isopropyl, and diisopropyl ketones obtainable by oxidation of the secondary branched chain aliphatic alcohols produced by the catalytic pressure hydrogenation of oxide of carbon.

5. In plastic sheeting operations, the method of softening but not dissolving sheeting of nitrocellulose plastic compositions which comprises treating such compositions with a solution of about one part by volume of water and 3 to 4 parts of a solution comprising about 87 parts of methanol and about 13 parts of diisopropyl ketone.

JULIUS F. T. BERLINER. 

